Four-piece infrared single wavelength lens system

ABSTRACT

A four-piece infrared single wavelength lens system includes, in order from the object side to the image side: a first lens element with a positive refractive power, a stop, a second lens element with a refractive power, a third lens element with a positive refractive power, and a fourth lens element with a negative refractive power. The focal length of the first lens element is f1, the focal length of the second lens element and the third lens element combined is f23, and they satisfy the relation: 0.05&lt;f1/f23&lt;1.8. When the above relation is satisfied, a wide field of view can be obtained and the resolution can be improved evidently.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a lens system, and more particularly toa miniaturized four-piece infrared single wavelength lens systemapplicable to electronic products.

Description of the Prior Art

Nowadays digital imaging technology is constantly innovating andchanging, in particular, digital carriers, such as, digital camera andmobile phone and so on, have become smaller in size, so CCD (ChargeCoupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensoris also required to be more compact. In addition to be used in the fieldof photography, in recent years, infrared focusing lens has also be usedin infrared receiving and sensing field of the game machine, and inorder to make the scope of game machine induction user more broader,wide-angle lens group has become the mainstream for receiving infraredwavelength at present.

The applicant has also put forward a number of lens groups related toinfrared wavelength reception, such as the single focus wide-angle lensmodules disclosed in TW Appl. Nos. 098100552, 098125378 and U.S. Pat.Nos. 8,031,413, 8,369,031, however, at present, the game machine isbased on a more three-dimensional, real and immediate 3D game, thecurrent or the applicant's previous lens groups are all 2D plane games,which cannot meet the 3D game focusing on the deep induction efficacy.

Special infrared receiving and induction lens groups for game machinesare made of plastic for the pursuit of low cost, however, poor materialtransparency is one of the key factors that affect the depth detectionaccuracy of the game machine, and plastic lenses are easy to overheat ortoo cold in ambient temperature, so that the focal length of the lensgroup will be changed and cannot focus accurately. Therefore, thecurrent infrared receiving and induction lens groups cannot meet the 3Dgame depth precise induction requirement.

The present invention mitigates and/or obviates the aforementioneddisadvantages.

SUMMARY OF THE INVENTION

The present invention is aimed at providing a four-piece infrared singlewavelength lens system which has a wide field of view, high resolution,short length and less distortion.

Therefore, a four-piece infrared single wavelength lens system inaccordance with the present invention comprises, in order from an objectside to an image side: a first lens element with a positive refractivepower, having an object-side surface being convex near an optical axisand an image-side surface being concave near the optical axis, at leastone of the object-side surface and the image-side surface of the firstlens element being aspheric; a stop; a second lens element with arefractive power, having an object-side surface being convex near theoptical axis and an image-side surface being concave near the opticalaxis, at least one of the object-side surface and the image-side surfaceof the second lens element being aspheric; a third lens element with apositive refractive power having an object-side surface being concavenear the optical axis and an image-side surface being convex near theoptical axis, at least one of the object-side surface and the image-sidesurface of the third lens element being aspheric; and a fourth lenselement with a negative refractive power having an object-side surfacebeing concave near the optical axis and an image-side surface beingconcave near the optical axis, at least one of the object-side surfaceand the image-side surface of the fourth lens element being aspheric andprovided with at least one inflection point.

A focal length of the first lens element is f1, a focal length of thesecond lens element and the third lens element combined is f23, and theysatisfy the relation: 0.05<f1/f23<1.8.

When the above relation is satisfied, a wide field of view can beobtained and the resolution can be improved evidently.

Preferably, the focal length of the first lens element is f1, a focallength of the second lens element is f2, and they satisfy the relation:−0.15<f1/f2<0.25, so that the refractive power of the first lens elementand the second lens element are more suitable, it will be favorable toobtain a wide field of view and avoid the excessive increase ofaberration of the system.

Preferably, the focal length of the second lens element is f2, a focallength of the third lens element is f3, and they satisfy the relation:−14<f2/f3<46, so that the refractive power of the second lens elementand the third lens element are more balanced, it will be favorable tocorrect the aberration of the system and reduce the sensitivity of thesystem.

Preferably, the focal length of the third lens element is f3, a focallength of the fourth lens element is f4, and they satisfy the relation:−16<f3/f4<−1.0, so that the refractive power of the system can bebalanced effectively, it will be favorable to reduce the sensitivity ofthe system, improving the yield of production.

Preferably, the focal length of the first lens element is f1, the focallength of the third lens element is f3, and they satisfy the relation:0.05<f1/f3<1.8, so that the positive refractive power of the first lenselement can be distributed effectively, so as to reduce the sensitivityof the four-piece infrared single wavelength lens system.

Preferably, the focal length of the second lens element is f2, the focallength of the fourth lens element is f4, and they satisfy the relation:−65<f2/f4<20, so that the positive refractive power of the system ismore suitable, it will be favorable to correct the aberration of thesystem and improve the image quality.

Preferably, a focal length of the first lens element and the second lenselement combined is f12, the focal length of the third lens element isf3, and they satisfy the relation: 0.05<f12/f3<1.8.

Preferably, the focal length of the first lens element and the secondlens element combined is f12, a focal length of the third lens elementand the fourth lens element combined is f34, and they satisfy therelation: −1.0<f12/f34<−0.2, which is favorable to obtain a wide fieldof view and effectively correct image distortion.

Preferably, the focal length of the first lens element is f1, a focallength of the second lens element, the third lens element and the fourthlens element combined is f234, and they satisfy the relation:−1.0<f1/f234<−0.2, which is favorable to obtain a wide field of view andeffectively correct image distortion.

Preferably, the four-piece infrared single wavelength lens system has amaximum view angle FOV, and it satisfies the relation: 50<FOV<80, sothat the four-piece infrared single wavelength lens system will have anappropiately large field of view.

Preferably, a central thickness of the second lens element along theoptical axis is CT2, a distance along the optical axis between thesecond lens element and the third lens element is T23, and they satisfythe relation: 0.4<CT2/T23<1.0, so that the thickness of the second lenselement and the distance between the lens elements are more suitable,which can effectively reduce the total length of the lens system.

Preferably, the distance along the optical axis between the second lenselement and the third lens element is T23, a central thickness of thethird lens element along the optical axis is CT3, and they satisfy therelation: 0.2<T23/CT3<1.3, so that the height of the off-axis incidentlight passing through the second and third lens elements is relativelylarge, and the third lens element has sufficient capacity to correct thefield curve, distortion and coma aberration of the four-piece infraredsingle wavelength lens system, which is favorable to correct the imagequality.

Preferably, the central thickness of the third lens element along theoptical axis is CT3, a distance along the optical axis between the thirdlens element and the fourth lens element is T34, and they satisfy therelation: 0.5<CT3/T34<3.3, so that the thickness of the third lenselement and the distance between the lens elements are more suitable,which can effectively reduce the total length of the lens system.

Preferably, an Abbe number of the first lens element is V1, an Abbenumber of the second lens element is V2, and they satisfy the relation:30<V1−V2<42, which can reduce the chromatic aberration of the four-pieceinfrared single wavelength lens system effectively.

The present invention will be presented in further details from thefollowing descriptions with the accompanying drawings, which show, forpurpose of illustrations only, the preferred embodiments in accordancewith the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a four-piece infrared single wavelength lens system inaccordance with a first embodiment of the present invention;

FIG. 1B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the first embodimentof the present invention;

FIG. 2A shows a four-piece infrared single wavelength lens system inaccordance with a second embodiment of the present invention;

FIG. 2B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the second embodimentof the present invention;

FIG. 3A shows a four-piece infrared single wavelength lens system inaccordance with a third embodiment of the present invention;

FIG. 3B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the third embodimentof the present invention;

FIG. 4A shows a four-piece infrared single wavelength lens system inaccordance with a fourth embodiment of the present invention;

FIG. 4B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the fourth embodimentof the present invention;

FIG. 5A shows a four-piece infrared single wavelength lens system inaccordance with a fifth embodiment of the present invention; and

FIG. 5B shows the longitudinal spherical aberration curve, theastigmatic field curve and the distortion curve of the fifth embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1A and 1B, FIG. 1A shows a four-piece infrared singlewavelength lens system in accordance with a first embodiment of thepresent invention, and FIG. 1B shows, in order from left to right, thelongitudinal spherical aberration curves, the astigmatic field curves,and the distortion curve of the first embodiment of the presentinvention. A four-piece infrared single wavelength lens system inaccordance with the first embodiment of the present invention comprisesa stop 100 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 110, a second lenselement 120, a third lens element 130, a fourth lens element 140, an IRcut filter 170, and an image plane 180, wherein the four-piece infraredsingle wavelength lens system has a total of four lens elements withrefractive power. The stop 100 is disposed between an image-side surface112 of the first lens element 110 and an image-side surface 122 of thesecond lens element 120.

The first lens element 110 with a positive refractive power has anobject-side surface 111 being convex near an optical axis 190 and theimage-side surface 112 being concave near the optical axis 190, theobject-side surface 111 and the image-side surface 112 are aspheric, andthe first lens element 110 is made of plastic material.

The second lens element 120 with a positive refractive power has anobject-side surface 121 being convex near the optical axis 190 and theimage-side surface 122 being concave near the optical axis 190, theobject-side surface 121 and the image-side surface 122 are aspheric, andthe second lens element 120 is made of plastic material.

The third lens element 130 with a positive refractive power has anobject-side surface 131 being concave near the optical axis 190 and animage-side surface 132 being convex near the optical axis 190, theobject-side surface 131 and the image-side surface 132 are aspheric, andthe third lens element 130 is made of plastic material.

The fourth lens element 140 with a negative refractive power has anobject-side surface 141 being concave near the optical axis 190 and animage-side surface 142 being concave near the optical axis 190, theobject-side surface 141 and the image-side surface 142 are aspheric, andthe fourth lens element 140 is made of plastic material, and at leastone of the object-side surface 141 and the image-side surface 142 isprovided with at least one inflection point.

The IR cut filter 170 made of glass is located between the fourth lenselement 140 and the image plane 180 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The equation for the aspheric surface profiles of the respective lenselements of the first embodiment is expressed as follows:

${z = {\frac{{ch}^{2}}{1 + \left\lbrack {1 - {\left( {k + 1} \right)c^{2}h^{2}}} \right\rbrack^{0.5}} + {Ah}^{4} + {Bh}^{6} + {Ch}^{8} + {Dh}^{10} + {Eh}^{12} + {Gh}^{14} + \ldots}}\mspace{14mu}$

wherein:

z represents the value of a reference position with respect to a vertexof the surface of a lens and a position with a height h along theoptical axis 190;

c represents a paraxial curvature equal to 1/R (R: a paraxial radius ofcurvature);

h represents a vertical distance from the point on the curve of theaspheric surface to the optical axis 190;

k represents the conic constant;

A, B, C, D, E, G, . . . : represent the high-order asphericcoefficients.

In the first embodiment of the present four-piece infrared singlewavelength lens system, a focal length of the four-piece infrared singlewavelength lens system is f, a f-number of the four-piece infraredsingle wavelength lens system is Fno, the four-piece infrared singlewavelength lens system has a maximum view angle (field of view) FOV, andthey satisfy the relations: f=4.437 mm; Fno=2.4; and FOV=69 degrees.

In the first embodiment of the present four-piece infrared singlewavelength lens system, a focal length of the first lens element 110 isf1, a focal length of the second lens element 120 and the third lenselement 130 combined is f23, and they satisfy the relation:f1/f23=0.617.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the first lens element 110is f1, a focal length of the second lens element 120 is f2, and theysatisfy the relation: f1/f2=0.147.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the second lens element 120is f2, a focal length of the third lens element 130 is f3, and theysatisfy the relation: f2/f3=3.473.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the third lens element 130is f3, a focal length of the fourth lens element 140 is f4, and theysatisfy the relation: f3/f4=−2.027.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the first lens element 110is f1, the focal length of the third lens element 130 is f3, and theysatisfy the relation: f1/f3=0.510.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the second lens element 120is f2, the focal length of the fourth lens element 140 is f4, and theysatisfy the relation: f2/f4=−7.039.

In the first embodiment of the present four-piece infrared singlewavelength lens system, a focal length of the first lens element 110 andthe second lens element 120 combined is f12, the focal length of thethird lens element 130 is f3, and they satisfy the relation:f12/f3=0.448.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the first lens element 110and the second lens element 120 combined is f12, a focal length of thethird lens element 130 and the fourth lens element 140 combined is f34,and they satisfy the relation: f12/f34=−0.449.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the focal length of the first lens element isf1, a focal length of the second lens element 120, the third lenselement 130 and the fourth lens element 140 combined is f234, and theysatisfy the relation: f1/f234=−0.320.

In the first embodiment of the present four-piece infrared singlewavelength lens system, a central thickness of the second lens element120 along the optical axis 190 is CT2, a distance along the optical axis190 between the second lens element 120 and the third lens element 130is T23, and they satisfy the relation: CT2/T23=0.817.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the distance along the optical axis 190 betweenthe second lens element 120 and the third lens element 130 is T23, acentral thickness of the third lens element 130 along the optical axis190 is CT3, and they satisfy the relation: T23/CT3=0.901.

In the first embodiment of the present four-piece infrared singlewavelength lens system, the central thickness of the third lens element130 along the optical axis 190 is CT3, a distance along the optical axis190 between the third lens element 130 and the fourth lens element 140is T34, and they satisfy the relation: CT3/T34=0.718.

In the first embodiment of the present four-piece infrared singlewavelength lens system, an Abbe number of the first lens element 110 isV1, an Abbe number of the second lens element 120 is V2, and theysatisfy the relation: V1-V2=32.03.

The detailed optical data of the first embodiment is shown in table 1,and the aspheric surface data is shown in table 2.

TABLE 1 Embodiment 1 f(focal length) = 4.437 mm, Fno = 2.4, FOV = 69deg. Curvature Focal surface Radius Thickness Material Index Abbe #length 0 object infinity 800.000 1 infinity 0.000 2 Lens 1 1.311 (ASP)0.728 plastic 1.544 56.000 4.421 3 2.361 (ASP) 0.230 4 stop infinity0.020 5 Lens 2 3.989 (ASP) 0.351 plastic 1.636 23.970 30.131 6 4.911(ASP) 0.429 7 Lens 3 −2.304 (ASP) 0.477 plastic 1.636 23.970 8.676 8−1.737 (ASP) 0.663 9 Lens 4 −3.525 (ASP) 0.596 plastic 1.544 56.000−4.281 10 6.977 (ASP) 0.895 11 IR-filter infinity 0.210 glass 1.51064.167 — 12 infinity 0.075 13 Image infinity 0.000 plane

TABLE 2 Aspheric Coefficients surface 2 3 5 6 K: 1.5275E−01 −5.2423E+00−3.6456E+01 1.4391E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 B:−1.0141E−02 5.5191E−02 −3.1672E−03 −1.5782E−02 C: 2.8477E−03 −2.1654E−02−1.8133E−02 −1.0686E−01 D: 4.1395E−03 −1.0322E−02 −2.1030E−01 2.9937E−01E: −2.9832E−02 7.8199E−02 3.2802E−01 −5.0325E−01 F: 2.6228E−021.5643E−02 −3.6030E−02 4.3308E−01 G 0.0000E+00 0.0000E+00 0.0000E+000.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 surface 7 8 910 K: −3.3566E+01 −8.0934E−01 −1.0649E+00 2.6389E+00 A: 0.0000E+000.0000E+00 0.0000E+00 0.0000E+00 B: −3.2793E−01 4.3562E−02 −9.1622E−02−1.0074E−01 C: 5.4027E−01 −7.9936E−02 5.7737E−02 3.6252E−02 D:−8.5200E−01 2.1179E−01 −1.0913E−02 −1.0129E−02 E: 8.0629E−01 −1.7691E−014.9966E−04 1.4882E−03 F: −4.1792E−01 6.3594E−02 3.3172E−05 −8.5898E−05 G−5.4280E−03 −9.9235E−03 0.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+000.0000E+00 0.0000E+00

The units of the radius of curvature, the thickness and the focal lengthin table 1 are expressed in mm, the surface numbers 0-13 represent thesurfaces sequentially arranged from the object-side to the image-sidealong the optical axis. In table 2, k represents the conic coefficientof the equation of the aspheric surface profiles, and A, B, C, D, E, F,G, H . . . : represent the high-order aspheric coefficients. The tablespresented below for each embodiment are the corresponding schematicparameter and aberration curves, and the definitions of the tables arethe same as Table 1 and Table 2 of the first embodiment. Therefore, anexplanation in this regard will not be provided again.

Referring to FIGS. 2A and 2B, FIG. 2A shows a four-piece infrared singlewavelength lens system in accordance with a second embodiment of thepresent invention, and FIG. 2B shows, in order from left to right, thelongitudinal spherical aberration curves, the astigmatic field curves,and the distortion curve of the second embodiment of the presentinvention. A four-piece infrared single wavelength lens system inaccordance with the second embodiment of the present invention comprisesa stop 200 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 210, a second lenselement 220, a third lens element 230, a fourth lens element 240, an IRcut filter 270, and an image plane 280, wherein the four-piece infraredsingle wavelength lens system has a total of three lens elements withrefractive power. The stop 200 is disposed between an image-side surface212 of the first lens element 210 and an image-side surface 222 of thesecond lens element 220.

The first lens element 210 with a positive refractive power has anobject-side surface 211 being convex near an optical axis 290 and theimage-side surface 212 being concave near the optical axis 290, theobject-side surface 211 and the image-side surface 212 are aspheric, andthe first lens element 210 is made of plastic material.

The second lens element 220 with a positive refractive power has anobject-side surface 221 being convex near the optical axis 290 and theimage-side surface 222 being concave near the optical axis 290, theobject-side surface 221 and the image-side surface 222 are aspheric, andthe second lens element 220 is made of plastic material.

The third lens element 230 with a positive refractive power has anobject-side surface 231 being concave near the optical axis 290 and animage-side surface 232 being convex near the optical axis 290, theobject-side surface 231 and the image-side surface 232 are aspheric, andthe third lens element 230 is made of plastic material.

The fourth lens element 240 with a negative refractive power has anobject-side surface 241 being concave near the optical axis 290 and animage-side surface 242 being concave near the optical axis 290, theobject-side surface 241 and the image-side surface 242 are aspheric, andthe fourth lens element 240 is made of plastic material, and at leastone of the object-side surface 241 and the image-side surface 242 isprovided with at least one inflection point.

The IR cut filter 270 made of glass is located between the fourth lenselement 240 and the image plane 280 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The detailed optical data of the second embodiment is shown in table 3,and the aspheric surface data is shown in table 4.

TABLE 3 Embodiment 2 f(focal length) = 4.445 mm, Fno = 2.4, FOV = 68deg. Curvature Focal surface Radius Thickness Material Index Abbe #length 0 object infinity 800.000 1 infinity 0.000 2 Lens 1 1.274 (ASP)0.780 plastic 1.544 56.000 3.722 3 2.767 (ASP) 0.264 4 stop infinity0.092 5 Lens 2 29.428 (ASP) 0.329 plastic 1.636 23.970 81.482 6 70.818(ASP) 0.451 7 Lens 3 −3.463 (ASP) 0.435 plastic 1.544 56.000 56.796 8−3.246 (ASP) 0.662 9 Lens 4 −6.030 (ASP) 0.671 plastic 1.544 56.000−4.048 10 3.525 (ASP) 0.529 11 IR-filter infinity 0.210 glass 1.51064.167 — 12 infinity 0.077 13 Image infinity 0.000 plane

TABLE 4 Aspheric Coefficients surface 2 3 5 6 K: 3.6889E−01 −2.4207E+00 4.6622E+01 −5.0705E+01  A: 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00B: −6.2078E−03  8.5293E−02 −2.9603E−02  −5.0669E−02  C: −6.7200E−02 −1.6764E−01  −1.6155E−01  −4.6051E−02  D: 1.1158E−01 8.0729E−016.1796E−01 2.0741E−01 E: −1.0965E−01  −1.4196E+00  −8.6181E−01 −4.0841E−01  F: 3.4886E−02 1.2978E+00 6.6529E−01 4.3669E−01 G 0.0000E+000.0000E+00 0.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+000.0000E+00 surface 7 8 9 10 K: −7.2612E+00  4.0417E+00 −3.6141E+01 −4.0876E+01  A: 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 B:−2.2125E−01  −7.8337E−02  −2.2157E−01  −9.8465E−02  C: 1.2355E−017.5000E−02 1.3687E−01 3.3099E−02 D: −4.0046E−01  −3.4062E−02 −3.6937E−02  −7.3378E−03  E: 4.1312E−01 1.5471E−02 4.9224E−03 8.1625E−04F: −3.4437E−01  −2.8597E−03  −2.6314E−04  −3.2649E−05  G 0.0000E+000.0000E+00 0.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+000.0000E+00

In the second embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the second embodiment, so an explanationin this regard will not be provided again.

Moreover, these parameters can be calculated from Table 3 and Table 4 asthe following values and satisfy the following conditions:

Embodiment 2 f 4.445 f12/f3 0.063 Fno 2.4 f12/f34 −0.851 FOV 68 f1/f230.108 f1/f2 0.046 f1/f234 −0.814 f2/f3 1.435 CT2/T23 0.731 f3/f4 −14.031T23/CT3 1.037 f1/f3 0.066 CT3/T34 0.656 f2/f4 −20.129 V1 − V2 32.030

Referring to FIGS. 3A and 3B, FIG. 3A shows a four-piece infrared singlewavelength lens system in accordance with a third embodiment of thepresent invention, and FIG. 3B shows, in order from left to right, thelongitudinal spherical aberration curves, the astigmatic field curves,and the distortion curve of the third embodiment of the presentinvention. A four-piece infrared single wavelength lens system inaccordance with the third embodiment of the present invention comprisesa stop 300 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 310, a second lenselement 320, a third lens element 330, a fourth lens element 340, an IRcut filter 370, and an image plane 380, wherein the four-piece infraredsingle wavelength lens system has a total of four lens elements withrefractive power. The stop 300 is disposed between an image-side surface312 of the first lens element 310 and an image-side surface 322 of thesecond lens element 320.

The first lens element 310 with a positive refractive power has anobject-side surface 311 being convex near an optical axis 390 and theimage-side surface 312 being concave near the optical axis 390, theobject-side surface 311 and the image-side surface 312 are aspheric, andthe first lens element 310 is made of plastic material.

The second lens element 320 with a positive refractive power has anobject-side surface 321 being convex near the optical axis 390 and theimage-side surface 322 being concave near the optical axis 390, theobject-side surface 321 and the image-side surface 322 are aspheric, andthe second lens element 320 is made of plastic material.

The third lens element 330 with a positive refractive power has anobject-side surface 331 being concave near the optical axis 390 and animage-side surface 332 being convex near the optical axis 390, theobject-side surface 331 and the image-side surface 332 are aspheric, andthe third lens element 330 is made of plastic material.

The fourth lens element 340 with a negative refractive power has anobject-side surface 341 being concave near the optical axis 390 and animage-side surface 342 being concave near the optical axis 390, theobject-side surface 341 and the image-side surface 342 are aspheric, andthe fourth lens element 340 is made of plastic material, and at leastone of the object-side surface 341 and the image-side surface 342 isprovided with at least one inflection point.

The IR cut filter 370 made of glass is located between the fourth lenselement 340 and the image plane 380 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The detailed optical data of the third embodiment is shown in table 5,and the aspheric surface data is shown in table 6.

TABLE 5 Embodiment 3 f(focal length) = 4.491 mm, Fno = 2.4, FOV = 68deg. Curvature Focal surface Radius Thickness Material Index Abbe #length 0 object infinity 800.000 1 infinity 0.000 2 Lens 1 1.372 (ASP)0.843 plastic 1.544 56.000 4.361 3 2.606 (ASP) 0.162 4 stop infinity0.105 5 Lens 2 4.095 (ASP) 0.350 plastic 1.636 23.970 36.627 6 4.839(ASP) 0.433 7 Lens 3 −2.660 (ASP) 0.389 plastic 1.636 23.970 9.612 8−1.938 (ASP) 0.573 9 Lens 4 −4.383 (ASP) 0.663 plastic 1.636 23.970−4.269 10 6.960 (ASP) 0.895 11 IR-filter infinity 0.210 glass 1.51064.167 — 12 infinity 0.075 13 Image infinity 0.000 plane

TABLE 6 Aspheric Coefficients surface 2 3 5 6 K: 8.1160E−02 −7.4271E+00 −4.9678E+01 −1.1307E+01  A: 0.0000E+00 0.0000E+00  0.0000E+00 0.0000E+00B: −8.6497E−03  3.9108E−02 −2.1013E−02 −3.6265E−02  C: −6.0209E−03 −4.4722E−02  −4.1191E−02 −1.3270E−01  D: 9.8734E−03 4.5570E−03−2.0905E−01 2.9832E−01 E: −1.6709E−02  7.0047E−02  3.9413E−01−4.8983E−01  F: 8.0128E−03 −4.7047E−02  −1.1814E−01 4.0681E−01 G0.0000E+00 0.0000E+00  0.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 surface 7 8 9 10 K: −5.4696E+01  −3.7927E−01 −5.3525E−02  −1.5617E+00  A: 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00B: −3.4334E−01  8.2219E−03 −1.1857E−01  −1.0495E−01  C: 5.2882E−014.8017E−03 7.7436E−02 3.8599E−02 D: −8.7206E−01  6.0831E−02 −1.8065E−02 −1.0410E−02  E: 7.6893E−01 −3.9802E−02  1.7800E−03 1.4348E−03 F:−3.9038E−01  4.7576E−03 −5.2416E−05  −7.4041E−05  G 0.0000E+000.0000E+00 0.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+000.0000E+00

In the third embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the third embodiment, so an explanation inthis regard will not be provided again.

Moreover, these parameters can be calculated from Table 5 and Table 6 asthe following values and satisfy the following conditions:

Embodiment 3 f 4.491 f12/f3 0.407 Fno 2.4 f12/f34 −0.491 FOV 68 f1/f230.543 f1/f2 0.119 f1/f234 −0.388 f2/f3 3.811 CT2/T23 0.808 f3/f4 −2.251T23/CT3 1.114 f1/f3 0.454 CT3/T34 0.679 f2/f4 −8.579 V1 − V2 32.030

Referring to FIGS. 4A and 4B, FIG. 4A shows a four-piece infrared singlewavelength lens system in accordance with a fourth embodiment of thepresent invention, and FIG. 4B shows, in order from left to right, thelongitudinal spherical aberration curves, the astigmatic field curves,and the distortion curve of the fourth embodiment of the presentinvention. A four-piece infrared single wavelength lens system inaccordance with the fourth embodiment of the present invention comprisesa stop 400 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 410, a second lenselement 420, a third lens element 430, a fourth lens element 440, an IRcut filter 470, and an image plane 480, wherein the four-piece infraredsingle wavelength lens system has a total of four lens elements withrefractive power. The stop 400 is disposed between an image-side surface412 of the first lens element 410 and an image-side surface 422 of thesecond lens element 420.

The first lens element 410 with a positive refractive power has anobject-side surface 411 being convex near an optical axis 490 and theimage-side surface 412 being concave near the optical axis 490, theobject-side surface 411 and the image-side surface 412 are aspheric, andthe first lens element 410 is made of plastic material.

The second lens element 420 with a negative refractive power has anobject-side surface 421 being convex near the optical axis 490 and theimage-side surface 422 being concave near the optical axis 490, theobject-side surface 421 and the image-side surface 422 are aspheric, andthe second lens element 420 is made of plastic material.

The third lens element 430 with a positive refractive power has anobject-side surface 431 being concave near the optical axis 490 and animage-side surface 432 being convex near the optical axis 490, theobject-side surface 431 and the image-side surface 432 are aspheric, andthe third lens element 430 is made of plastic material.

The fourth lens element 440 with a negative refractive power has anobject-side surface 441 being concave near the optical axis 490 and animage-side surface 442 being concave near the optical axis 490, theobject-side surface 441 and the image-side surface 442 are aspheric, andthe fourth lens element 440 is made of plastic material, and at leastone of the object-side surface 441 and the image-side surface 442 isprovided with at least one inflection point.

The IR cut filter 470 made of glass is located between the fourth lenselement 440 and the image plane 480 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The detailed optical data of the fourth embodiment is shown in table 7,and the aspheric surface data is shown in table 8.

TABLE 7 Embodiment 4 f(focal length) = 5.152 mm, Fno = 2.4, FOV = 60deg. Curvature Focal surface Radius Thickness Material Index Abbe #length 0 object infinity 3500.000 1 infinity 0.000 2 Lens 1 1.629 (ASP)0.940 plastic 1.544 56.000 4.621 3 3.798 (ASP) 0.212 4 stop infinity0.202 5 Lens 2 5.467 (ASP) 0.397 plastic 1.651 21.500 −58.294 6 4.624(ASP) 0.739 7 Lens 3 −3.342 (ASP) 0.673 plastic 1.651 21.500 4.654 8−1.682 (ASP) 0.423 9 Lens 4 −2.547 (ASP) 0.398 plastic 1.544 56.000−3.298 10 6.097 (ASP) 1.040 11 IR-filter infinity 0.300 glass 1.51064.167 — 12 infinity 0.075 13 Image infinity 0.000 plane

TABLE 8 Aspheric coefficients surface 2 3 5 6 K: 4.1677E−02 −1.1787E+01 −7.3391E+01  −1.3302E+01  A: 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00B: −4.4462E−03  1.7241E−02 −1.4376E−02  −2.7514E−02  C: 3.6939E−04−1.2258E−02  −5.4798E−02  −1.2222E−02  D: −2.7547E−04  1.4958E−039.8825E−03 1.3654E−02 E: −7.0930E−04  6.4545E−03 3.6441E−02 −7.9882E−03 F: 4.0972E−04 −3.6931E−03  −2.1053E−02  1.4253E−02 G 0.0000E+000.0000E+00 0.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+000.0000E+00 surface 7 8 9 10 K: −1.6471E+01  −8.3310E−01  −1.4832E+01 4.6380E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 B:−8.1916E−02  7.3770E−02 −1.7799E−02  −5.0973E−02  C: 2.2476E−03−3.3017E−02  5.7906E−03 8.7924E−03 D: −1.9998E−02  1.1462E−02 3.9734E−04−1.7400E−03  E: 9.3137E−03 −1.9769E−03  −3.2079E−04  1.7056E−04 F:−8.9328E−03  4.5253E−06 3.1683E−05 −7.3552E−06  G 0.0000E+00 0.0000E+000.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00

In the fourth embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the fourth embodiment, so an explanationin this regard will not be provided again.

Moreover, these parameters can be calculated from Table 7 and Table 8 asthe following values and satisfy the following conditions:

Embodiment 4 f 5.152 f12/f3 1.016 Fno 2.4 f12/f34 −0.376 FOV 60 f1/f230.911 f1/f2 −0.079 f1/f234 −0.449 f2/f3 −12.527 CT2/T23 0.537 f3/f4−1.411 T23/CT3 1.099 f1/f3 0.993 CT3/T34 1.591 f2/f4 17.678 V1 − V234.500

Referring to FIGS. 5A and 5B, FIG. 5A shows a four-piece infrared singlewavelength lens system in accordance with a fifth embodiment of thepresent invention, and FIG. 5B shows, in order from left to right, thelongitudinal spherical aberration curves, the astigmatic field curves,and the distortion curve of the fifth embodiment of the presentinvention. A four-piece infrared single wavelength lens system inaccordance with the fifth embodiment of the present invention comprisesa stop 500 and a lens group. The lens group comprises, in order from anobject side to an image side: a first lens element 510, a second lenselement 520, a third lens element 530, a fourth lens element 540, an IRcut filter 570, and an image plane 580, wherein the four-piece infraredsingle wavelength lens system has a total of four lens elements withrefractive power. The stop 500 is disposed between an image-side surface512 of the first lens element 510 and an image-side surface 522 of thesecond lens element 520.

The first lens element 510 with a positive refractive power has anobject-side surface 511 being convex near an optical axis 590 and theimage-side surface 512 being concave near the optical axis 590, theobject-side surface 511 and the image-side surface 512 are aspheric, andthe first lens element 510 is made of plastic material.

The second lens element 520 with a positive refractive power has anobject-side surface 521 being convex near the optical axis 590 and theimage-side surface 522 being concave near the optical axis 590, theobject-side surface 521 and the image-side surface 522 are aspheric, andthe second lens element 520 is made of plastic material.

The third lens element 530 with a positive refractive power has anobject-side surface 531 being concave near the optical axis 590 and animage-side surface 532 being convex near the optical axis 590, theobject-side surface 531 and the image-side surface 532 are aspheric, andthe third lens element 530 is made of plastic material.

The fourth lens element 540 with a negative refractive power has anobject-side surface 541 being concave near the optical axis 590 and animage-side surface 542 being concave near the optical axis 590, theobject-side surface 541 and the image-side surface 542 are aspheric, andthe fourth lens element 540 is made of plastic material, and at leastone of the object-side surface 541 and the image-side surface 542 isprovided with at least one inflection point.

The IR cut filter 570 made of glass is located between the fourth lenselement 540 and the image plane 580 and has no influence on the focallength of the four-piece infrared single wavelength lens system.

The detailed optical data of the fifth embodiment is shown in table 9,and the aspheric surface data is shown in table 10.

TABLE 9 Embodiment 5 f(focal length) = 4.403 mm, Fno = 2.4, FOV = 70deg. Curvature Focal surface Radius Thickness Material Index Abbe #length 0 object infinity 3500.000 1 infinity 0.000 2 Lens 1 1.595 (ASP)0.890 plastic 1.544 56.000 4.819 3 3.355 (ASP) 0.121 4 stop infinity0.156 5 Lens 2 5.024 (ASP) 0.365 plastic 1.651 21.500 128.762 6 5.206(ASP) 0.470 7 Lens 3 −9.806 (ASP) 1.467 plastic 1.636 23.970 2.904 8−1.600 (ASP) 0.468 9 Lens 4 −1.667 (ASP) 0.445 plastic 1.651 21.500−2.036 10 6.097 (ASP) 0.544 11 IR-filter infinity 0.300 glass 1.51064.167 — 12 infinity 0.075 13 Image infinity 0.000 plane

TABLE 10 Aspheric coefficients surface 2 3 5 6 K: 3.4283E−02−8.7586E+00  −5.8159E+01 −1.9890E+01  A: 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 B: 1.1032E−04 1.8469E−02 −2.5303E−02 −2.9337E−02 C: 4.7704E−03 −1.0791E−02  −6.3546E−02 −1.7596E−02  D: −2.9726E−03 −8.6025E−03  −1.8315E−02 3.4571E−03 E: 2.9195E−03 2.3480E−02  6.5390E−026.2710E−03 F: 2.6712E−05 −2.2376E−02  −4.2075E−02 1.1995E−02 G0.0000E+00 0.0000E+00  0.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 surface 7 8 9 10 K: −3.6186E+01  −9.1698E−01 −5.5972E+00  3.7657E+00 A: 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00B: −3.8366E−02  6.8827E−02 −1.5878E−02  −3.9438E−02  C: 5.1598E−03−2.4100E−02  8.6910E−03 9.4188E−03 D: −1.2022E−02  1.0584E−02−2.6359E−04  −1.9771E−03  E: −4.0816E−04  −2.0709E−03  −2.0253E−04 2.2033E−04 F: 1.9043E−03 9.4568E−05 1.7584E−05 −1.0637E−05  G 0.0000E+000.0000E+00 0.0000E+00 0.0000E+00 H 0.0000E+00 0.0000E+00 0.0000E+000.0000E+00

In the fifth embodiment, the equation of the aspheric surface profilesof the aforementioned lens elements is the same as the equation of thefirst embodiment. Also, the definitions of these parameters shown in thefollowing table are the same as those stated in the first embodimentwith corresponding values for the fifth embodiment, so an explanation inthis regard will not be provided again.

Moreover, these parameters can be calculated from Table 9 and Table 10as the following values and satisfy the following conditions:

Embodiment 5 f 4.403 f12/f3 1.573 Fno 2.4 f12/f34 −0.392 FOV 70 f1/f231.631 f1/f2 0.037 f1/f234 −0.354 f2/f3 44.343 CT2/T23 0.777 f3/f4 −1.426T23/CT3 0.320 f1/f3 1.660 CT3/T34 3.134 f2/f4 −63.243 V1 − V2 34.500

In the present four-piece infrared single wavelength lens system, thelens elements can be made of plastic or glass. If the lens elements aremade of plastic, the cost will be effectively reduced. If the lenselements are made of glass, there is more freedom in distributing therefractive power of the four-piece infrared single wavelength lenssystem. Plastic lens elements can have aspheric surfaces, which allowmore design parameter freedom (than spherical surfaces), so as to reducethe aberration and the number of the lens elements, as well as the totaltrack length of the four-piece infrared single wavelength lens system.

In the present four-piece infrared single wavelength lens system, if theobject-side or the image-side surface of the lens elements withrefractive power is convex and the location of the convex surface is notdefined, the object-side or the image-side surface of the lens elementsnear the optical axis is convex. If the object-side or the image-sidesurface of the lens elements is concave and the location of the concavesurface is not defined, the object-side or the image-side surface of thelens elements near the optical axis is concave.

The four-piece infrared single wavelength lens system of the presentinvention can be used in focusing optical systems and can obtain betterimage quality. The four-piece infrared single wavelength lens system ofthe present invention can also be used in electronic imaging systems,such as, 3D image capturing, digital camera, mobile device, digital flatpanel or vehicle camera.

While we have shown and described various embodiments in accordance withthe present invention, it should be clear to those skilled in the artthat further embodiments may be made without departing from the scope ofthe present invention.

1. A four-piece infrared single wavelength lens system, in order from anobject side to an image side, comprising: a first lens element with apositive refractive power, having an object-side surface being convexnear an optical axis and an image-side surface being concave near theoptical axis, at least one of the object-side surface and the image-sidesurface of the first lens element being aspheric; a stop; a second lenselement with a refractive power, having an object-side surface beingconvex near the optical axis and an image-side surface being concavenear the optical axis, at least one of the object-side surface and theimage-side surface of the second lens element being aspheric; and athird lens element with a positive refractive power, having anobject-side surface being concave near the optical axis an image-sidesurface being convex near the optical axis, at least one of theobject-side surface and the image-side surface of the third lens elementbeing aspheric; and a fourth lens element with a negative refractivepower, having an object-side surface being concave near the optical axisan image-side surface being concave near the optical axis, at least oneof the object-side surface and the image-side surface of the fourth lenselement being aspheric and provided with at least one inflection point;wherein a focal length of the first lens element is f1, a focal lengthof the second lens element and the third lens element combined is f23,and they satisfy the relation: 0.05<f1/f23<1.8.
 2. The four-pieceinfrared single wavelength lens system as claimed in claim 1, whereinthe focal length of the first lens element is f1, a focal length of thesecond lens element is f2, and they satisfy the relation:−0.15<f1/f2<0.25.
 3. The four-piece infrared single wavelength lenssystem as claimed in claim 1, wherein a focal length of the second lenselement is f2, a focal length of the third lens element is f3, and theysatisfy the relation: −14<f2/f3<46.
 4. The four-piece infrared singlewavelength lens system as claimed in claim 1, wherein a focal length ofthe third lens element is f3, a focal length of the fourth lens elementis f4, and they satisfy the relation: −16<f3/f4<−1.0.
 5. The four-pieceinfrared single wavelength lens system as claimed in claim 1, whereinthe focal length of the first lens element is f1, a focal length of thethird lens element is f3, and they satisfy the relation: 0.05<f1/f3<1.8.6. The four-piece infrared single wavelength lens system as claimed inclaim 1, wherein a focal length of the second lens element is f2, afocal length of the fourth lens element is f4, and they satisfy therelation: −65<f2/f4<20.
 7. The four-piece infrared single wavelengthlens system as claimed in claim 1, wherein a focal length of the firstlens element and the second lens element combined is f12, a focal lengthof the third lens element is f3, and they satisfy the relation:0.05<f12/f3<1.8.
 8. The four-piece infrared single wavelength lenssystem as claimed in claim 1, wherein a focal length of the first lenselement and the second lens element combined is f12, a focal length ofthe third lens element and the fourth lens element combined is f34, andthey satisfy the relation: −1.0<f12/f34<−0.2.
 9. The four-piece infraredsingle wavelength lens system as claimed in claim 1, wherein the focallength of the first lens element is f1, a focal length of the secondlens element, the third lens element and the fourth lens elementcombined is f234, and they satisfy the relation: −1.0<f1/f234<−0.2. 10.The four-piece infrared single wavelength lens system as claimed inclaim 1, wherein the four-piece infrared single wavelength lens systemhas a maximum view angle FOV, and it satisfies the relation: 50<FOV<80.11. The four-piece infrared single wavelength lens system as claimed inclaim 1, wherein a central thickness of the second lens element alongthe optical axis is CT2, a distance along the optical axis between thesecond lens element and the third lens element is T23, and they satisfythe relation: 0.4<CT2/T23<1.0.
 12. The four-piece infrared singlewavelength lens system as claimed in claim 1, wherein a distance alongthe optical axis between the second lens element and the third lenselement is T23, a central thickness of the third lens element along theoptical axis is CT3, and they satisfy the relation: 0.2<T23/CT3<1.3. 13.The four-piece infrared single wavelength lens system as claimed inclaim 1, wherein a central thickness of the third lens element along theoptical axis is CT3, a distance along the optical axis between the thirdlens element and the fourth lens element is T34, and they satisfy therelation: 0.5<CT3/T34<3.3.
 14. The four-piece infrared single wavelengthlens system as claimed in claim 1, wherein an Abbe number of the firstlens element is V1, an Abbe number of the second lens element is V2, andthey satisfy the relation: 30<V1−V2<42.